Fast registration : do not use last name in user name

I created the attached patch to fulfill a need on one of my sites :
- Instead of using "FirstName LastName" when using fast registration, I want to be able to use "FirstName L." for the sake of privacy of my users
- When using Drupal Commons, I want to fill the fields "First Name" and "Last Name" of the profile module with the correct values from Facebook

I created a checkbox in the "appearance" settings part of facebook connect that allows you to unlock this feature.

I'm sure this can't go mainstream as is, but maybe we can build something generic from it.